Topic 1

• Energy is never used up. Instead it's just transferred between different energy stores and different objects
• Energy is Transferred Between Stores

  When energy is transferred to an object, the energy is stored in one of the object's energy stores
• Energy stores you need to know

  • Thermal energy stores
  • Kinetic energy stores
  • Gravitational potential energy stores
  • Elastic potential energy stores
  • Chemical energy stores
  • Magnetic energy stores
  • Electrostatic energy stores
  • Nuclear energy stores
• System

  A fancy word for a single object or a group of objects that you're interested in
• When a system changes, energy is transferred. It can be transferred into or away from the system, between different objects in the system or between different types of energy stores
• Closed system


  A system where neither matter nor energy can enter or leave
• The net change in the total energy of a closed system is always zero
• Energy can be Transferred by Heating


  1. Energy is transferred to the water's thermal energy store (causing the temperature of the water to rise)

  2. Energy is transferred electrically to the thermal energy store of the kettle's heating element, which transfers energy by heating to the water's thermal energy store
• Work done

  Another way of saying energy transferred - they're the same thing
• Work can be done

  • When current flows (work is done against resistance in a circuit)
  • By a force moving an object
• Falling Objects Also Transfer Energy

  1. The gravitational force does work

  2. As it falls, energy from the object's gravitational potential energy store is transferred to its kinetic energy store
• For a falling object when there's no air resistance: energy lost from the gravitational potential energy store = energy gained in the kinetic energy store
• Kinetic energy

  Energy in an object's kinetic energy store
• Gravitational potential energy

  Energy in an object's gravitational potential energy store
• Elastic potential energy


  Energy in an object's elastic potential energy store
• Specific heat capacity


  How hard it is to heat something up
• Investigating Specific Heat Capacity

  1. Measure the mass of the block

  2. Wrap it in an insulating layer and insert the thermometer and heater

  3. Measure the initial temperature and set the potential difference

  4. Turn on the power supply and start a stopwatch

  5. Measure the block's temperature every minute

  6. Calculate the power supplied to the heater and the energy transferred

  7. Plot a graph of energy transferred against temperature and find the gradient
• Energy is never destroyed. Energy can be transferred usefully, stored or dissipated, but can never be created or destroyed
• Dissipated energy

  Energy that is being stored in a way that is not useful (usually energy has been transferred into thermal energy stores)
• When energy is transferred between stores, not all of the energy is transferred usefully into the store that you want it to go to. Some energy is always dissipated when an energy transfer takes place
• Power

  The rate of energy transfer, or the rate of doing work
• A powerful machine is one which transfers a lot of energy in a short space of time
• Conduction

  The process where vibrating particles transfer energy to neighbouring particles
• Conduction occurs mainly in solids
• When you add heat to an object, the energy is transferred to the thermal energy store of the object
• The particles in the part of the object being heated become more energetic and collide with each other more
• This increased collision transfers energy between the particles' kinetic energy stores
• The energy is then gradually handed to the thermal energy store of the rest of the object
• Thermal conductivity is a measure of how quickly energy is transferred through a material
• Some substances are better thermal conductors than others
• Good conductors allow energy to be transferred quickly between their particles
• Poor conductors have particles that are further apart, so less energy is transferred
• Convection

  Where energetic particles move away from hotter to cooler regions
• Convection occurs only in liquids and gases
• When you heat a region of a gas or liquid, the particles move faster and the space between individual particles increases
• This causes the density of the region being heated to decrease
• The warmer and less dense region will rise above denser, cooler regions
• If there is a constant heat source, a convection current can be created
• How a radiator creates convection currents

  1. Energy is transferred from the radiator to the nearby air particles by conduction

  2. The air by the radiator becomes warmer and less dense

  3. This warm air rises and is replaced by cooler air

  4. The previously heated air transfers energy to the surroundings and cools, becoming denser and sinking

  5. This cycle repeats, causing a flow of air to circulate around the room
• Lubrication can be used to reduce the friction between objects' surfaces when they move